The coordinated activity of various organs and tissues provides the body with stability and vitality. The supreme regulator of the activity of all organs of our body and, first of all, the heart and blood vessels is the cerebral cortex. The lower parts of the brain, which are usually called the subcortex, are subordinate to it. It concentrates reflex activity, to a certain extent independent of the will of a person.

It ensures the implementation of the so-called unconditioned reflexes - instincts (food, defensive, etc.), plays big role in the manifestation of emotions - fear, anger, joy, etc. No less important for the activity of the subcortex is the regulation of the most important vital functions of the body - blood circulation, respiration, digestion, metabolism, etc.

The corresponding centers located in the subcortex are connected with various internal organs and tissues, in particular with the cardiovascular system, through the so-called autonomic, or autonomic, nervous system. Under the influence of excitation of one of its two departments - sympathetic or parasympathetic (wandering), the work of the heart changes in different directions and blood vessels.

From various organs that need an increased blood flow, “signals” go to the central nervous system, and from it the corresponding impulses are sent to the heart and blood vessels. As a result, the supply of blood to the organs is either increased or weakened, depending on their needs.

The autonomic nervous system has a great influence on activity of cardio-vascular system... The terminal branches of the sympathetic and vagus nerves are directly connected with the nodes in the heart muscle described above and through them affect the frequency, rhythm and strength of heart contractions.

Excitation of the sympathetic nerves causes the heart to beat faster. In this case, the conduction of an impulse through the muscle of the heart is also accelerated, the blood vessels (except for the heart) narrow, blood pressure rises.

Irritation vagus nerve reduces the excitability of the sinus node, so the heart beats less frequently. In addition, the conduction of the impulse along the atrioventricular bundle slows down (sometimes significantly), and with very sharp irritation of the vagus nerve, the impulse is sometimes not conducted at all, and therefore there is a disconnection between the atria and ventricles (the so-called blockade).

Under normal conditions, that is, with a moderate effect on the heart, the vagus nerve provides it with peace. Therefore, IP Pavlov said about the vagus nerve that "to a certain extent it can be called the nerve of rest, the nerve that regulates the rest of the heart."

The autonomic nervous system constantly affects the heart and blood vessels, influencing the frequency and strength of heart contractions, as well as the size of the lumen of the blood vessels. The heart and blood vessels are also involved in numerous reflexes that arise under the influence of irritations coming from the external environment or from the body itself. So, for example, heat speeds up the heart rate and dilates blood vessels, cold makes the heart beat slower, narrows the skin vessels and therefore causes pallor.

When we move or do hard physical work, the heart beats faster and more forcefully, and when we are at rest, it beats less frequently and weaker. The heart can stop due to reflex irritation of the vagus nerve with a strong blow to the abdomen. The very severe pain experienced with various injuries of the body, also in the order of a reflex, can lead to excitation of the vagus nerve and, consequently, to the fact that the heart will begin to contract less frequently.

When excited (by verbal and other stimuli) of the cerebral cortex and subcortical regions, for example, with strong fear, joy and other emotions, one or another part of the autonomic nervous system - the sympathetic or parasympathetic (vagus) nerve. In this regard, the heart beats more often, then less often, then stronger, then weaker, the blood vessels then narrow, then expand, the person turns red and then turns pale.

The glands are usually involved in this. internal secretion, which are themselves under the influence of the sympathetic and vagus nerves and in turn act on these nerves with hormones.

From all that has been said, it is clear how multifaceted, multifaceted is the connection of the cardiovascular system with nervous and chemical regulators, how great is the power of the nerves over the cardiovascular system.

The autonomic nervous system is under the direct influence of the brain, from which streams of various impulses constantly go to it, exciting either the sympathetic or the vagus nerve. The "leading" role of the cerebral cortex in the regulation of the work of all organs is also reflected in the fact that the activity of the heart changes depending on the body's need for blood supply. A healthy adult heart at rest beats 60-80 times per minute. It takes during diastole (relaxation) and throws about 60-80 milliliters (cubic centimeters) of blood into the vessels during systole (contraction). And with great physical exertion, when hard working muscles need an increased supply of blood, the amount of blood thrown out with each contraction can significantly increase (in a well-trained athlete, up to 2000 milliliters or even more).

We told how the heart works, how the frequency and strength of heart contractions change. But how does blood circulation occur throughout the body, how does blood move through the vessels of the whole organism, what forces make it move all the time in a certain direction, at a certain speed, which maintains the pressure inside the blood vessels necessary for the constant movement of blood?

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When do prophetic dreams occur?

Sufficiently clear images from a dream make an indelible impression on the awakened person. If after some time the events in a dream are embodied in reality, then people are convinced that this dream was prophetic. Prophetic dreams differ from ordinary ones in that, with rare exceptions, they have a direct meaning. Prophetic dream always bright, memorable ...

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The autonomic nervous system (systema nervosum autonomicum; synonym: autonomic nervous system, involuntary nervous system, visceral nervous system) is a part of the nervous system that provides activity internal organs, regulation of vascular tone, innervation of glands, trophic innervation of skeletal muscles, receptors and the nervous system itself. By interacting with the somatic (animal) nervous system and endocrine system, it ensures the maintenance of constancy of homeostasis and adaptation to changing environmental conditions. The autonomic nervous system has central and peripheral divisions. In the central section, there are suprasegmental (higher) and segmental (lower) vegetative centers.

Suprasegmental autonomic centers are concentrated in the brain - in the cerebral cortex (mainly in the frontal and parietal lobes), hypothalamus, olfactory brain, subcortical structures (striatum), in the brain stem (reticular formation), cerebellum, etc. Segmental autonomic centers are located both in the brain and in the spinal cord. The vegetative centers of the brain are conventionally subdivided into the midbrain and bulbar (the vegetative nuclei of the oculomotor, facial, lingopharyngeal and vagus nerves), and the spinal cord into the lumbar-sternum and sacral (the nuclei of the lateral horns of the segments CVIII-LIII and SII-SIV, respectively). The motor centers of innervation of non-striated (smooth) muscles of internal organs and blood vessels are located in the precentral and frontal regions. There are also centers of reception from internal organs and blood vessels, centers of perspiration, nervous trophism, metabolism.

Centers of thermoregulation, salivation and lacrimation are concentrated in the striatum. The participation of the cerebellum in the regulation of such autonomic functions as the pupillary reflex and skin trophism was established. Kernels reticular formation make up suprasegmental centers of vital functions - respiratory, vasomotor, cardiac activity, swallowing, etc. Peripheral department V. of N. with. represented by nerves and nodes located near the internal organs (extramurally) or in their thickness (intramurally). The vegetative nodes are interconnected by nerves, forming plexuses, for example, the pulmonary, cardiac, abdominal aortic plexus. On the basis of functional differences in V. of N. with. there are two divisions - sympathetic and parasympathetic.

The sympathetic nervous system includes segmental autonomic centers, the neurons of which are located in the lateral horns of 16 segments of the spinal cord (from CVIII to LIII), their axons (white, preganglionic, connecting branches) come out with the anterior roots of the corresponding 16 spinal nerves from the spinal canal and approach nodes (ganglia) of the sympathetic trunk; the sympathetic trunk is a chain of 17-22 pairs of interconnected vegetative nodes on both sides of the spine along its entire length. The nodes of the sympathetic trunk are connected by gray (postganglionic) connecting branches with all spinal nerves, visceral (organ) branches with prevertebral (prevertebral) and (or) organ autonomic nerve plexuses (or nodes). The prevertebral plexuses are located around the aorta and its large branches (thoracic aortic, celiac plexus, etc.), organ plexuses - on the surface of the internal organs (heart, gastrointestinal tract), as well as in their thickness (Fig.).

The parasympathetic nervous system includes autonomic centers embedded in the brain stem and represented by parasympathetic nuclei III, VII, IX, X pairs cranial nerves, as well as vegetative centers in the lateral horns of the SII-IV segments of the spinal cord. Preganglionic fibers from these centers are composed of III, VII (large stony, tympanic string), IX (small stony) and X pairs of cranial nerves to the parasympathetic nodes in the head area - ciliary, pterygo-palatine, ear, submandibular and parasympathetic nodes of the vagus nerve lying in the walls of organs (for example, nodes of the submucosal plexus of the intestinal wall). Postganglionic parasympathetic fibers extend from these nodes to the innervated organs. From the parasympathetic centers in the sacral region of the spinal cord, the pelvic visceral nerves go to the organ vegetative plexuses of the pelvic organs and the terminal sections of the colon (descending and sigmoid colon, rectum), which contain both sympathetic and parasympathetic neurons.

Physiology. The morphological basis of autonomic reflexes are reflex arcs, the simplest of which consists of three neurons. The first neuron - afferent (sensitive) - is located in the spinal nodes and in the nodes of the cranial nerves, the second neuron - the intercalary - in the segmental autonomic centers, and the third - efferent - in the autonomic nodes. In addition to the sensory neurons of the spinal nodes and nodes of the cranial nerves. V. n. with. has its own sensitive neurons located in the autonomic nodes. With their participation, two-neuronal reflex arcs are closed, which are of great importance in the autonomous (without the participation of c.ns.) regulation of the functions of internal organs.

The main function of V. n. with. consists in maintaining the constancy of the internal environment, or homeostasis, with various influences on the body. This function is carried out due to the process of emergence, transmission, perception and processing of information as a result of excitation of receptors of internal organs (interoception). At the same time V. n. with. regulates the activity of organs and systems that are not directly involved in maintaining homeostasis (for example, genitals, intraocular muscles, etc.), and also contributes to the provision of subjective sensations, various mental functions. Many internal organs receive both sympathetic and parasympathetic innervation. The influence of these two departments is often antagonistic in nature, but there are many examples when both departments of V. n. with. act synergistically (the so-called functional synergy). In many organs that have both sympathetic and parasympathetic innervation, in physiological conditions, the regulatory influences of parasympathetic nerves predominate. These organs include the bladder and some exocrine glands (lacrimal, digestive, etc.). There are also organs supplied with only sympathetic or only parasympathetic nerves; almost all blood vessels, spleen, smooth muscles eyes, some exocrine glands (sweat) and smooth muscles of the hair follicles.

With an increase in the tone of the sympathetic nervous system, heart contractions intensify and their rhythm quickens, the speed of excitation through the heart muscle increases, blood pressure rises, blood glucose increases, bronchi expand. pupils, the secretory activity of the adrenal medulla increases, the tone of the gastrointestinal tract decreases. An increase in the tone of the parasympathetic nervous system is accompanied by a decrease in the strength and frequency of heart contractions, a slowdown in the rate of conduction of excitation through the myocardium. A decrease in blood pressure, an increase in insulin secretion and a decrease in the concentration of glucose in the blood, an increase in the secretory and motor activity of the gastrointestinal tract. Under the action of a nerve impulse, acetylcholine is released at the endings of all preganglionic fibers and most postganglionic parasympathetic neurons, and adrenaline and norepinephrine, belonging to catecholamines, are released at the endings of sympathetic postganglionic neurons, in connection with which these neurons are called adrenergic.

The reactions of various organs to norepinephrine and adrenaline are mediated by the interaction of catecholamines with special formations of cell membranes - adrenergic receptors. Norepinephrine and acetylcholine, apparently, are not the only mediators of the peripheral V. of N. with. To substances that are attributed to the function of mediators of pre- and postganglionic sympathetic neurons, or which modulate the effect on synaptic transmission in V. n. N of page, also include histamine, substance P and other polypeptides, prostaglandin E and serotonin. Most of the internal organs, along with the existence of extraganglionic (sympathetic and parasympathetic), spinal and higher cerebral mechanisms of regulation, have their own local nervous mechanism of regulation of functions. The presence of common features in the structural and functional organization, as well as the data of onto- and phylogenesis allow many researchers to distinguish in the composition of V. n. with. (in the peripheral region), in addition to the sympathetic and parasympathetic systems, there is also a third - metasympathetic. The metasympathetic system combines a complex of microganglionic formations located in the walls of internal organs with motor activity (heart, ureters, gastrointestinal tract, etc.). The terminals of the axons of neurons located in the ganglia of the metasympathetic system contain ATP as mediators.

Many pre- and postganglionic autonomic neurons, which innervate, in particular, the blood vessels and the heart, exhibit spontaneous activity or resting tone. This tone is essential for the regulation of the functions of internal organs. There are viscero-visceral, viscero-somatic and viscerosensory reflexes. In the viscero-visceral reflex, excitement arises and ends in the internal organs, and the effector is able to respond by strengthening or inhibition of the function. for example, irritation of the carotid or aortic zone entails certain changes in the intensity of respiration, blood pressure, and heart rate.

In the viscero-somatic reflex, excitation, in addition to the visceral, also induces somatic responses in the form of, for example, protective muscle tension. abdominal wall with some pathological processes in organs abdominal... With the viscerosensory reflex, in response to irritation of autonomic afferent fibers, reactions occur in the internal organs, the somatic muscular system, as well as changes in somatic sensitivity. Viscerosomatic and viscerosensory reflexes have diagnostic value with some diseases of internal organs, in which tactile and pain sensitivity increases and pains appear in certain limited areas of the skin (see Zakharyina - Geda zone). There are also somatovisceral reflexes arising from the activation of exteroreceptors and somatic afferent fibers. These include, for example, galvanic skin reflex, vasoconstriction or dilatation during thermal effects on skin receptors, Danielopolu's clinostatic reflex, Ashner-Danini's ophthalmic reflex, Prevel's orthostatic reflex.

At irritation of fibers V. of N. with. you can also observe the so-called axon reflex, or pseudo-reflex. for example, antidromic excitation of thin fibers from skin pain receptors as a result of irritation of the peripheral segment of the cut dorsal root leads to vasodilation and reddening of the skin area innervated by these fibers. Like somatic nerves, autonomic nerves are projected onto several areas of the cerebral cortex, located next to the somatic projections and layered on them. The latter is necessary to ensure complex cardiovascular, respiratory and other reflexes. V.'s influence of n. with. on the autonomic functions of the body is realized in three main ways: through retonary changes in vascular tone, adaptive-trophic action and control of the functions of the heart, gastrointestinal tract, adrenal glands, and others. the page, providing the tone of the blood vessels, are located in the reticular formation of the medulla oblongata and the pons. The vasoconstrictor and heart rate accelerating centers, influencing the sympathetic nervous system, maintain the main vascular tone, to a lesser extent, the heart tone.

The vasodilating and inhibitory centers of the heart rhythm act indirectly both through the vasoconstrictor center, which depress, and by stimulating the posterior motor nucleus of the vagus nerve (in the case of an inhibitory effect on the heart). The tone of the vasomotor (vasomotor) centers is influenced by baro- and chemoreceptor stimuli emanating from both specific reflexogenic zones (carotid sinus, endocardoaortic zone, etc.) and from other formations. This tone is controlled by the overlying centers in the reticular formation, in the hypothalamus, olfactory brain, and cerebral cortex. Vasoconstriction is widely known when the sympathetic trunk is irritated. Some parasympathetic fibers (tympanic cord, pudendal nerve), fibers from the posterior roots of the spinal cord and sympathetic nerves of the vessels of the heart and skeletal muscles (their action is blocked by atropine) have a vasodilatory effect.

Influence of the sympathetic nervous system on c.ns. is manifested by a change in its bioelectric activity, as well as its conditioned and unconditioned reflex activity. In accordance with the theory of the adaptive-trophic influence of the sympathetic nervous system L.A. Orbeli distinguish two interrelated sides: the first is adaptation, which determines the functional parameters of the working organ, and the second, which ensures the maintenance of these parameters through physical and chemical changes in the level of tissue metabolism. The pathways of transmission of adaptive trophic influences are based on direct and indirect types of sympathetic innervation. There are tissues endowed with direct sympathetic innervation (heart muscle, uterus, and other smooth muscle formations), but the bulk of tissues (skeletal muscles, glands) have indirect adrenergic innervation. In this case, the transfer of the adaptive-trophic influence occurs humoral: the mediator is transferred to the effector cells by the blood stream or reaches them by diffusion.

In the implementation of the adaptive-trophic functions of the sympathetic nervous system, catecholamines are of particular importance. They are able to quickly and intensively influence metabolic processes, changing the level of glucose in the blood and stimulating the breakdown of glycogen, fats, increase the efficiency of the heart, ensure the redistribution of blood in different areas, increase the excitement of the nervous system, and promote the occurrence of emotional reactions. Research methods include the determination of autonomic reflexes (see Reflexes), the study of dermographism, sweating, Zakharyin-Ged zones, capillaroscopy, plethysmography, rheography, etc., as well as the study of respiratory function and cardiac activity (see Cardiovascular system, Heart) ... The data of these studies make it possible to establish the localization and nature of damage to the autonomic nervous system.

Pathology. Manifestations of V.'s defeat of N. with. are diverse and are largely determined by which of its departments is predominantly involved in the pathological process. Lesions of the autonomic plexuses, for example, the celiac, or solar, plexus (see Solaritis), ganglia (see Ganglionitis), are characterized by painful sensations different localization and intensity, a disorder of the functions of the associated internal organs, which can imitate acute illness heart, abdominal organs, small pelvis. Recognition of V.'s disease of N. with. perhaps in these cases only by exclusion during a detailed examination of the patient. Defeat of central departments V. of N. page, as a rule, is manifested by generalized violations of V.'s regulatory activity. with., disorder of adaptation of the organism to changing environmental conditions (for example, fluctuations in atmospheric pressure, humidity and air temperature, etc.), a decrease in working capacity, endurance to physical and mental stress.

Autonomic disorders are part of a complex of functional (for example, hysteria, neurasthenia) or organic lesions of the nervous system as a whole, and not just its vegetative section (for example, with traumatic brain injury, etc.). The defeat of the hypothalamus is characterized by the occurrence of hypothalamic syndromes. Dysfunction of the higher autonomic centers (hypothalamus and limbic system) can be accompanied by relatively selective disorders associated with disorders of the autonomic innervation of the vessels, primarily arteries - the so-called angiotrophoneuroses. Dysfunctions of the higher autonomic centers include sleep disturbances in the form of constant or paroxysmal drowsiness, the latter is often accompanied by emotional disorders (malice, aggressiveness), and pathological increase appetite, various endocrinopathies, obesity, etc. childhood a manifestation of such autonomic dysfunction may be bedwetting.

Treatment V.'s defeats of n. with. is determined by the reasons that caused them, as well as the localization of the lesion, the nature of the main clinical manifestations. Due to the fact that development vegetative disorders contribute to alcohol abuse and smoking, violations of the regime of work and rest, suffered infectious diseases, essential means prevention of V.'s diseases. with. are the correct organization of work and rest, hardening, sports. Tumors of the autonomic nervous system are relatively rare and arise from elements such as peripheral V. of N. with. and her central department... V.'s tumors of N. with. are benign and malignant. Neoplasms from elements of the peripheral department of V. of N. with. are tumors of the sympathetic ganglia, or neuronal tumors. Benign tumor V. n. with. are ganglioneuroma (ganglioglioma, ganglionic neuroma, ganglionic neurofibroma, sympathetic-cytoma). It is more often localized in the posterior mediastinum, retroperitoneal space, in the pelvic cavity, in the adrenal glands, in the neck.

Much less often the tumor is located in the wall of the stomach, intestine, bladder... Macroscopically, the ganglioneuroma is more often represented by a node or lobular conglomerate of nodes of various degrees of density from a whitish fibrous tissue in a section with areas of myxomatosis. More than half of patients with ganglioneuroma are younger than 20 years old. Slow growth these tumors determine the gradual appearance and, depending on the localization of the features clinical symptoms... Tumors usually reach large sizes and masses, have an expansive growth, during which the corresponding organs are squeezed, which significantly affects the clinical manifestations. With ganglioneuroma, malformations such as cleft upper lip and hard palate, which confirms their common dysontogenetic origin. Treatment is only surgical.

Among malignant tumors sympathetic ganglia secrete neuroblastoma (sympathoblastoma, sympathogonioma), which occurs mainly in children. The tumor, as a rule, is associated with cells of the adrenal medulla or elements of the paravertebral sympathetic chain. It is characterized by rapid growth with early metastasis to the liver, skull bones, the lymph nodes, lungs. Combined treatment. The prognosis is poor. Ganglioneuroblastomas are tumors with varying degrees of malignancy. Often found in childhood. In most cases, there is an increased production of catecholamines, therefore, in clinical picture diseases associated with this disorder (eg, diarrhea) can be observed. Paraganglionic formations (glomus tumors) of the chemoreceptor apparatus of the vascular bed (aortic, carotid, jugular and other glomuses) can serve as a source of tumor growth and give rise to the so-called chemodectomas. or glomus tumors. The vast majority of these tumors are benign. Macroscopically, they are well demarcated and usually closely associated with the wall of the corresponding large vessel. Growth is slow.

Clinically, in addition to the presence of a tumor (for example, on the neck), headaches, dizziness are noted. When pressing on the tumor, local soreness and short-term fainting sometimes occur. In some cases, the course is asymptomatic. The leading diagnostic method for these tumors, in particular the area carotid arteries, is angiography. Surgical treatment of glomus tumors. See also Nervous systems.

Bibliography: Vein A.M., Solovieva A.D. and Kolosova O.A. Vegetovascular dystonia, M., 1981; Gusev E.I., Grechko V.E. and Burd G.S. Nervous diseases, p. 199, 547, M., 1988; Lobko P.I. et al. The autonomic nervous system. Atlas, Minsk, 1988; Nozdrachev A.D. Physiology of the autonomic nervous system, L., 1983, bibliogr .; Pathological and anatomical diagnostics of human tumors, ed. ON. Kraevsky and others, p. 86, M., 1982; Paches A.I. Tumors of the head and neck, p. 90, M., 1983; Human Physiology, ed. R. Schmidt and G. Tevs, trans. from English, v. 1, p. 167, M., 1985; Haulike I. Vegetative nervous system (Anatomy and physiology), trans. from Romanians., Bucharest, 1978, bibliogr.

Heart is abundant innervated organ... Among the sensitive formations of the heart, two populations of mechanoreceptors are of primary importance, concentrated mainly in the atria and the left ventricle: A receptors respond to changes in the tension of the heart wall, and B receptors are excited during its passive stretching. Afferent fibers associated with these receptors are part of the vagus nerves. Free sensory nerve endings, located directly under the endocardium, are the terminals of afferent fibers passing through the sympathetic nerves.

Efferent innervation of the heart carried out with the participation of both divisions of the autonomic nervous system. The bodies of sympathetic preganglionic neurons involved in the innervation of the heart are located in the gray matter of the lateral horns of the three upper thoracic segments of the spinal cord. Preganglionic fibers are directed to the neurons of the superior thoracic (stellate) sympathetic ganglion. The postganglionic fibers of these neurons, together with the parasympathetic fibers of the vagus nerve, form the upper, middle and lower cardiac nerves. Sympathetic fibers penetrate the entire organ and innervate not only the myocardium, but also the elements of the conducting system.

The bodies of parasympathetic preganglionic neurons involved in innervation of the heart... are located in the medulla oblongata. Their axons are part of the vagus nerves. After the vagus nerve enters the chest cavity, branches depart from it, which are included in the heart nerves.

The processes of the vagus nerve, which are part of the heart nerves, are parasympathetic preganglionic fibers... From them, excitation is transmitted to intramural neurons and then - mainly to the elements of the conducting system. The influences mediated by the right vagus nerve are mainly addressed to the cells of the sinoatrial, and the left ones - to the cells of the atrioventricular node. The vagus nerves do not have a direct effect on the ventricles of the heart.

Innervating the fabric of pacemakers... autonomic nerves are able to change their excitability, thereby causing changes in the frequency of generation of action potentials and heart contractions ( chronotropic effect ). Nervous influences change the rate of electrotonic transmission of excitation and, consequently, the duration of the phases of the cardiac cycle. Such effects are called dromotropic.

Since the action of mediators of the autonomic nervous system is to change the level of cyclic nucleotides and energy metabolism, autonomic nerves in general are able to influence the strength of heart contractions ( inotropic effect ). Under laboratory conditions, the effect of changing the value of the excitation threshold of cardiomyocytes under the action of neurotransmitters was obtained; it is designated as batmotropic.

The listed pathways of the nervous system on the contractile activity of the myocardium and the pumping function of the heart are, although extremely important, but secondary to myogenic mechanisms, modulating influences.

Innervation of the heart and blood vessels

The activity of the heart is regulated by two pairs of nerves: vagus and sympathetic (Fig. 32). The vagus nerves originate in the medulla oblongata, and the sympathetic nerves branch off from the cervical sympathetic node. The vagus nerves inhibit cardiac activity. If you start to irritate the vagus nerve with an electric current, then there is a slowdown and even arrest of heart contractions (Fig. 33). After the termination of the irritation of the vagus nerve, the work of the heart is restored.

Figure: 32. Scheme of innervation of the heart

Figure: 33. Influence of irritation of the vagus nerve on the heart of the frog

Figure: 34. Effect of irritation of the sympathetic nerve on the heart of the frog

Under the influence of impulses coming to the heart through the sympathetic nerves, the rhythm of cardiac activity increases and each heartbeat intensifies (Fig. 34). In this case, the systolic, or stroke, blood volume increases.

If the dog is in a calm state, his heart beats 50 to 90 times in 1 minute. If you cut all the nerve fibers heading to the heart, the heart now contracts 120-140 times per minute. If only the vagus nerves of the heart are cut, the heart rate will increase to 200-250 beats per minute. This is due to the influence of the preserved sympathetic nerves. The heart of man and many animals is under the constant restraining influence of the vagus nerves.

The vagus and sympathetic nerves of the heart usually act in concert: if the excitability of the center of the vagus nerve increases, then the excitability of the center of the sympathetic nerve decreases accordingly.

During sleep, in a state of physical rest of the body, the heart slows down its rhythm due to the strengthening of the influence of the vagus nerve and some decrease: the influence of the sympathetic nerve. During physical work, the heart rate increases. In this case, there is an increase in the influence of the sympathetic nerve and a decrease in the influence of the vagus nerve on the heart. In this way, an economical mode of operation of the heart muscle is ensured.

The change in the lumen of blood vessels occurs under the influence of impulses transmitted to the walls of the vessels along vasoconstrictor nerves. The impulses coming along these nerves arise in the medulla oblongata in vasomotor center... The opening and description of the activities of this center belongs to F.V. Ovsyannikov.

Ovsyannikov Philip Vasilievich (1827-1906) - an outstanding Russian physiologist and histologist, full member of the Russian Academy of Sciences, teacher I.P. Pavlova. FV Ovsyannikov studied the issues of blood circulation regulation. In 1871 he discovered the vasomotor center in the medulla oblongata. Ovsyannikov studied the mechanisms of respiration regulation, the properties of nerve cells, and contributed to the development of the reflex theory in domestic medicine.

Reflex influences on the activity of the heart and blood vessels

The rhythm and strength of the heartbeats vary depending on emotional state person, the work he does. The human condition also affects the blood vessels, changing their lumen. You often see how with fear, anger, physical stress, a person either turns pale, or, on the contrary, blushes.

The work of the heart and the lumen of the blood vessels are associated with the needs of the body, its organs and tissues in providing them with oxygen and nutrients. The adaptation of the activity of the cardiovascular system to the conditions in which the body is located is carried out by nervous and humoral regulatory mechanisms, which usually function in an interconnected manner. Nerve influences that regulate the activity of the heart and blood vessels are transmitted to them from the central nervous system along the centrifugal nerves. By irritation of any sensitive endings, you can reflexively cause a decrease or increase in heart rate. Heat, cold, an injection and other irritations cause excitement in the endings of the centripetal nerves, which is transmitted to the central nervous system and from there, along the vagus or sympathetic nerve, reaches the heart.

Test 15

Immobilize the frog so that it retains the medulla oblongata. Do not destroy the spinal cord! Pin the frog to the board, belly up. Bare your heart. Count the number of heartbeats in 1 min. Then use tweezers or scissors to hit the frog on the abdomen. Count the number of heartbeats in 1 min. The activity of the heart after a blow to the abdomen slows down or even temporarily stops. This happens reflexively. A blow to the abdomen causes excitation in the centripetal nerves, which reaches the center of the vagus nerves through the spinal cord. Hence, excitation along the centrifugal fibers of the vagus nerve reaches the heart and inhibits or stops its contraction.

Explain why the frog's spinal cord should not be destroyed in this experiment.

Is it possible to cause cardiac arrest in a frog when it hits the abdomen if the medulla oblongata is removed?

The centrifugal nerves of the heart receive impulses not only from the medulla oblongata and spinal cord, but also from the overlying parts of the central nervous system, including from the cerebral cortex. Pain is known to cause an increase in heart rate. If the child was given injections during treatment, then only the appearance of a white coat will cause an increase in heart rate. This is evidenced by the change in cardiac activity in athletes before the start, in pupils and students before exams.

Figure: 35. The structure of the adrenal glands: 1 - the outer, or cortical, layer in which hydrocortisone, corticosterone, aldosterone and other hormones are produced; 2 - the inner layer, or medulla, in which adrenaline and norepinephrine are formed

Impulses from the central nervous system are transmitted simultaneously along the nerves to the heart and from the vasomotor center along other nerves to the blood vessels. Therefore, usually the heart and blood vessels reflexively respond to irritation from the external or internal environment of the body.

Humoral regulation of blood circulation

The activity of the heart and blood vessels is influenced by chemicals in the blood. So, in the endocrine glands - the adrenal glands - a hormone is produced adrenalin (fig. 35). It speeds up and enhances the activity of the heart and narrows the lumen of the blood vessels.

In the nerve endings of the parasympathetic nerves is formed, acetylcholine... which expands the lumen of blood vessels and slows down and weakens cardiac activity. Some salts also affect the work of the heart. An increase in the concentration of potassium ions inhibits the work of the heart, and an increase in the concentration of calcium ions causes an increase in the rate of heart activity.

Humoral influences are closely related to the nervous regulation of the circulatory system. Highlighting chemical substances into the blood and maintaining a certain concentration in the blood is regulated by the nervous system.

The activity of the entire circulatory system is aimed at providing the body in different conditions with the necessary amount of oxygen and nutrients, removing metabolic products from cells and organs, maintaining blood pressure at a constant level. This creates conditions for maintaining the constancy of the internal environment of the body.

Innervation of the heart

The sympathetic innervation of the heart is carried out from the centers located in the lateral horns of the three upper thoracic segments of the spinal cord. Preganglionic nerve fibers emanating from these centers go to the cervical sympathetic ganglia and transmit excitation there to neurons, postganglionic fibers from which innervate all parts of the heart. These fibers transmit their influence on the structures of the heart with the help of the norepinephrine mediator and through the p-adrenergic receptors. Pi receptors predominate on the membranes of the contractile myocardium and the conducting system. There are about 4 times more of them than P2 receptors.

The sympathetic centers that regulate the work of the heart, in contrast to the parasympathetic ones, do not have a pronounced tone. An increase in impulses from the sympathetic nerve centers to the heart occurs periodically. For example, when these centers are activated, caused by reflex or descending influences from the centers of the trunk, hypothalamus, limbic system and cerebral cortex.

Reflex influences on the work of the heart are carried out from many reflexogenic zones, including from the receptors of the heart itself. In particular, an increase in myocardial tension and an increase in atrial pressure are an adequate stimulus for the so-called A-receptors of the atria. In the atria and ventricles, there are B-receptors that are activated when the myocardium is stretched. There are also pain receptorsinitiating severe pain with insufficient oxygen delivery to the myocardium (pain with a heart attack). Impulses from these receptors are transmitted to the nervous system through fibers passing in the vagus and branches of the sympathetic nerves.

Nervous regulation characterized by a number of features:

1. The nervous system has a starting and corrective effect on the work of the heart, providing adaptation to the needs of the body.

2. The nervous system regulates the intensity of metabolic processes.

The heart is innervated by fibers of the central nervous system (extracardiac mechanisms) and its own fibers (intracardiac). At the heart of the intracardiac regulation mechanisms is the metsympathetic nervous system, which contains all the necessary intracardiac formations for the occurrence of a reflex arc and the implementation of local regulation. An important role is played by the fibers of the parasympathetic and sympathetic divisions autonomic nervous system, providing afferent and efferent innervation. Efferent parasympathetic fibers are represented by vagus nerves, bodies of I preganglionic neurons located at the bottom of the rhomboid fossa of the medulla oblongata. Their processes end intramurally, and the bodies of II postganglionic neurons are located in the heart system. The vagus nerves provide innervation to the formations of the conducting system: the right one - the sinoatrial node, the left one - the atrioventricular. The centers of the sympathetic nervous system lie in the lateral horns of the spinal cord at the level of the I – V thoracic segments. It innervates the ventricular myocardium, atrial myocardium, the conducting system.

When the sympathetic nervous system is activated, the strength and heart rate change.

The centers of the nuclei that innervate the heart are in a state of constant moderate excitement, due to which nerve impulses come to the heart. The tone of the sympathetic and parasympathetic divisions is not the same. In an adult, the tone of the vagus nerves predominates. It is supported by impulses coming from the central nervous system from receptors embedded in vascular system... They lie in the form of nerve clusters reflex zones:

1.in the area of \u200b\u200bthe carotid sinus;

2. in the area of \u200b\u200bthe aortic arch;

3. in the area of \u200b\u200bcoronary vessels.

When the nerves coming from the carotid sinuses to the central nervous system are cut, there is a drop in the tone of the nuclei that innervate the heart.

The vagus and sympathetic nerves are antagonists and have 5 influences on the heart:

1.chronotropic (change the heart rate);

2. inotropic (change the force of heart contractions);

3. batmotropic (affect the excitability of the myocardium);

4. dromotropic (affects conductivity);

5. tonotropic (affect the tone of the myocardium).

That is, they affect the intensity of metabolic processes.

Parasympathetic nervous system - all 5 negative phenomena; sympathetic nervous system - all 5 phenomena are positive.

Homeometric regulation of the heart.

It turned out that the change in the force of heart contraction depends not only on the initial length of cardiomyocytes at the end of diastole. A number of studies have shown an increase in the force of contraction with an increase in heart rate against the background of the isometric state of the fibers. This is due to the fact that an increase in the frequency of contraction of cardiomyocytes leads to an increase in Ca2 content in the sarcoplasm of muscle fibers. All this improves the electromechanical coupling and leads to an increase in the contraction force.

Innervation of the heart and its regulation.

Modulation of inotropic, chronotropic and dromotropic effects is caused by the sympathetic and parasympathetic divisions of the autonomic nervous system. The cardiac nerves of the ANS are composed of two types of neurons. The bodies of the first neurons are located in the central nervous system, and the bodies of the second neurons form ganglia outside the central nervous system. Preganglionic fibers of sympathetic neurons are shorter than postganglionic ones, while in parasympathetic ones, vice versa.

Influence of the parasympathetic nervous system.

Parasympathetic regulation of the heart is carried out by the cardiac branches of the right and left vagus nerves (X pair of cranial nerves). The bodies of the first neurons are localized in the dorsal nucleus of the vagus nerve of the medulla oblongata. The axons of these neurons as part of the vagus nerve leave the cranial cavity and go to the intramural ganglia of the heart, where the bodies of the second neurons are located. Postganglionic fibers of the vagus nerve in most cases terminate in cardiomyocytes of the CA and AV nodes, atria and the intra-atrial conduction system. The right and left vagus nerves have different functional effects on the heart. The distribution area of \u200b\u200bthe right and left vagus nerves is not symmetrical and overlaps. The right vagus nerve affects mainly the SA node. Its stimulation causes a decrease in the frequency of excitation of the CA node. Whereas the left vagus nerve has a predominant effect on the AV node. Excitation of this nerve leads to varying degrees of atrioventricular block. The action of the vagus nerve on the heart is characterized by a very rapid response as well as its termination. This is due to the fact that the vagus mediator acetylcholine is rapidly destroyed by acetylcholinectrase, which is abundant in the CA and AV nodes. Moreover, acetylcholine acts through specific acetylcholine-regulating K "channels, which have a very short latency period (50-100 ms).